Hydrogen is used in a variety of applications, from ammonia synthesis to hydrogen vehicle operations. There will be a continuing and, likely, a large-scale increase in future demand for hydrogen from a large single train. To be suitable for delivery to pipelines, the hydrogen must be very pure and at a high pressure. Commonly, hydrogen is produced, purified, and then compressed to provide high pressure hydrogen for various uses. However, the compression of hydrogen is very expensive. The use of hydrogen for ammonia production is a well-established process. The commonly used methods of H2 production to produce the H2 to N2 mixture of 3 to 1 ratio generally result in the presence of additional inert impurities such as methane and argon being present in the gas mixture.
Ammonia is synthesized in a closed cycle catalytic reactor system with heat recovery and cooling of the circulating gas mixture to condense the ammonia which is removed from the loop as a liquid product. Any inert impurities which enter the loop with the fresh feed gas and which are in excess of the small quantity removed by dissolution in the liquid ammonia product must be removed by purging gas from the loop. Generally the impurity level is allowed to build up to about 15% molar in the circulating gas mixture leaving the ammonia condenser. This results in a serious loss of H2+N2 which must be separated from the inert components and optionally recompressed and returned to the ammonia synthesis loop. The pressure in the ammonia synthesis loop is in the range 100 bar to about 300 bar. The fresh H2+N2 feed must be compressed from the H2 generation pressure up to these high pressures.